This approach has been worked as an extension of the work of Chuang and Wang and Fletcher et al as a further step towards ``to teach a speech sound how the sound is made''[29]. The optopalatograph (OPG) is used as a device, which provides direct measurement of the distance between the hard palate and the tongue. The system is divided into three parts: 1) the optopalate itself, 2) a separate self contained unit composed of 16 switched infra-red light sources, associated control logic and 16 receivers, and 3) a computer with A/D card running software to analyse and interpret graphically the sensor outputs.
It displays the 3-dimensional oral cavity measures in the form of a selection of simultaneous 2-dimensional displays. These displays provide an applied focus for evaluation of the 3D potential before proceeding to the more complex 3D cavity volume or tongue surface modeling processes. These displays have the benefit of simplifying the 3D information for the learners. In this way, it is possible to represent the configuration of the tongue with respect to the hard palate more clearly and focus on regions of interest. This method is a subject of high-technological research in a newly-fledged field and as a rule requires expensive devices, but is quite effective.
